Abstract: A method is directed to a production of a bearing device for a wheel including an inner member and an outer member rotatable relative to each other through a plurality of rolling elements, in which a component part forming one of the inner member and the outer member is a hot forged product. In the practice of this method, during or at the end of a hot forging step for hot forging the component part, a portion of the component part is cooled by spraying a coolant or by controlling an atmospheric temperature, to thereby render a matrix of the component part to represent a standard structure and render a surface portion of the component part to represent a non-standard structure.

Abstract: A steel part having a long rolling contact fatigue life and capable of further increasing the life of a bearing under severer using condition than usual conditions. The steel part includes steel having a composition containing 0.7% by mass to 1.1% by mass of C, 0.5% by mass to 2.0% by mass of Si, 0.4% by mass to 2.5% by mass of Mn, 1.6% by mass to 5.0% by mass of Cr, 0.1% by mass to less than 0.5% by mass of Mo, 0.010% by mass to 0.050% by mass of Al, less than 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities, the steel being hardened and tempered. In the steel structure of a portion from the surface to a depth of 5 mm, residual cementite has a grain diameter of 0.05 to 1.5 ?m, prior austenite has a grain diameter of 30 ?m or less, and the ratio by volume of the residual austenite is less than 25%.

Abstract: A steel composition contains: 0.05% or less of C; 0.5% or less of Si; 0.20% to 1.80% of Mn; 0.03% or less of P; 0.005% or less of S; 14.0% to 18.0% of Cr; 5.0% to 8.0% of Ni; 1.5% to 3.5% of Mo; 0.5% to 3.5% of Cu; 0.05% or less of Al; 0.20% or less of V; 0.01% to 0.15% of N; and 0.006% or less of O on a mass basis, and satisfies the following expressions: Cr+0.65Ni+0.6Mo+0.55Cu?20C?18.5 and Cr+Mo+0.3Si?43.5C?0.4Mn?Ni?0.3Cu?9N?11 (where Cr, Ni, Mo, Cu, C, Si, Mn, and N represent their respective contents (mass %)). After such a steel pipe material is formed into a steel pipe, the steel pipe is quenched by cooling after heating to a temperature of the AC3 transformation point or more and tempered at a temperature of the AC1 transformation point or less.

Abstract: A hot forging facility enabling the manufacture of a hot forged product excellent in fatigue properties and cold workability is provided. A heating furnace for heating a steel material and a hot forging apparatus for performing forging of the heated steel material are sequentially arranged on a transport line. A partially cooling apparatus/apparatuses for partially cooling a forged product after hot forging is provided on an exit side of the hot forging apparatus.

Abstract: A hot forged product including hardened areas introduced by partial cooling after hot forging, and unhardened areas, wherein Vickers hardness V1 of the hardened areas on the surface and Vickers hardness V2 of the unhardened areas satisfy the following formula (1): (V1?V2)/V2: 0.1 to 0.8.

Abstract: A steel part having a long rolling contact fatigue life and capable of further increasing the life of a bearing under severer using condition than usual conditions. The steel part includes steel having a composition containing 0.7% by mass to 1.1% by mass of C, 0.5% by mass to 2.0% by mass of Si, 0.4% by mass to 2.5% by mass of Mn, 1.6% by mass to 5.0% by mass of Cr, 0.1% by mass to less than 0.5% by mass of Mo, 0.010% by mass to 0.050% by mass of Al, less than 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities, the steel being hardened and tempered. In the steel structure of a portion from the surface to a depth of 5 mm, residual cementite has a grain diameter of 0.05 to 1.5 ?m, prior austenite has a grain diameter of 30 ?m or less, and the ratio by volume of the residual austenite is less than 25%.

Abstract: We provide a steel product that includes, by mass %, C: 0.35-0.7%, Si: 0.30-1.1%, Mn: 0.2-2.0%, Al: 0.005-0.25%, Ti: 0.005-0.1%, Mo: 0.05-0.6%, B: 0.0003-0.006%, S: 0.06% or less, P: 0.02% or less, Cr: 0.2% or less, and the balance Fe and inevitable impurities, and has a structure of bainite and/or martensite, the total volume fraction of bainite and martensite being 10% or more, and an induction hardened member that is made of the steel product having a hardened surface layer formed by induction hardening and has a prior austenite grain size of 12 ?m or less through the layer thickness. The member has high fatigue strength and therefore is suitable for an automobile drive shaft, an automobile constant velocity joint or the like.

Abstract: A steel composition contains: 0.05% or less of C; 0.5% or less of Si; 0.20% to 1.80% of Mn; 0.03% or less of P; 0.005% or less of S; 14.0% to 18.0% of Cr; 5.0% to 8.0% of Ni; 1.5% to 3.5% of Mo; 0.5% to 3.5% of Cu; 0.05% or less of Al; 0.20% or less of V; 0.01% to 0.15% of N; and 0.006% or less of O on a mass basis, and satisfies the following expressions: Cr+0.65Ni+0.6Mo+0.55Cu?20C?18.5 and Cr+Mo+0.3Si?43.5C?0.4Mn?Ni?0.3Cu?9N?11 (where Cr, Ni, Mo, Cu, C, Si, Mn, and N represent their respective contents (mass %)). After such a steel pipe material is formed into a steel pipe, the steel pipe is quenched by cooling after heating to a temperature of the AC3 transformation point or more and tempered at a temperature of the AC1 transformation point or less. The composition may further contain at least one element of Nb and Ti; at least one element selected from the group consisting of Zr, B, and W; or Ca, singly or in combination.

Abstract: A steel pipe is produced by a method including performing diameter-reducing rolling on a steel pipe in a temperature range of from 600° C. to Ac3 with a reduction in diameter of not less than 30%, preferably after heating the steel pipe to temperatures of not lower than Ac1, the steel pipe being produced by seam-welding strip steel, or a method further including the step of performing heat treatment of holding the rolled steel pipe in a temperature range of from 600° C. to 900° C. for a time of 1 second or longer during cooling subsequent to the diameter-reducing rolling or by reheating the rolled steel pipe after the cooling.

Abstract: A hot forging facility enabling the manufacture of a hot forged product excellent in fatigue properties and cold workability is provided. A heating furnace for heating a steel material and a hot forging apparatus for perfonning forging of the heated steel material are sequentially arranged on a transport line. A partially cooling apparatus/apparatuses for partially cooling a forged product after hot forging is provided on an exit side of the hot forging apparatus.

Abstract: A method is directed to a production of a bearing device for a wheel including an inner member (1) and an outer member (2) rotatable relative to each other through a plurality of rolling elements (3), in which a component part forming one of the inner member (1) and the outer member (2) is a hot forged product. In the practice of this method, during or at the end of a hot forging step for hot forging the component part, a portion of the component part is cooled by spraying a coolant or by controlling an atmospheric temperature, to thereby render a matrix of the component part to represent a standard structure and render a surface portion of the component part to represent a non-standard structure (30).

Abstract: A hot forged product including hardened areas introduced by partial cooling after hot forging, and unhardened areas, wherein Vickers hardness V1 of the hardened areas on the surface and Vickers hardness V2 of the unhardened areas satisfy the following formula (1): (V1?V2)/V2: 0.1 to 0.8.

Abstract: A high-strength steel having excellent character of delayed fracture can be manufactured at a low cost without adding expensive alloy elements such as Ni, Co or V in large quantities. The steel including a steel microstructure in which a ratio of martensite phase is 90% or more and a diameter of prior austenite grains is 10 ?m or less, the steel microstructure being made by hardening and then tempering at 100° C. to 400° C., the steel including C: more than 0.30% and not more than 0.50% by mass, Si: not more than 1.0% by mass, Mn: not more than 1.5% by mass, Ti: not more than 0.1% by mass, Mo: not less than 0.3% and not more than 0.50% by mass, B: not less than 0.0005% and not more than 0.01% by mass, and a balance composed of Fe and inevitable impurities.

Abstract: There is provided a component for machine structure having a hardened layer through an induction hardening in at least a part thereof, and more improving fatigue strengths as compared with the conventional ones, in which the hardened layer has a hardness Hv of not less than 750 and an average grain size of prior austenite grains is not more than 7 ?m over a full thickness of the hardened layer.

Abstract: A steel for machine structural use with a better strength-ductility-toughness balance than maraging steel and applications thereof are provided. The steel for machine structural use with excellent strength, ductility, and toughness contains, in percent by mass, more than 0.30% to 0.5% of carbon, 1.0% or less of silicon, 1.5% or less of manganese, 0.025% or less of aluminum, 0.3% to 0.5% of molybdenum, and 0.0005% to 0.01% of boron, and the balance is iron and incidental impurities. The steel has a structure including at least 90% by volume of martensitic structure. The martensitic structure includes blocks having a size of 1.5 ?m or less. Dissolved boron is contained in an amount of at least 0.0005% and is present at boundaries of prior austenite grains in a concentration at least 1.5 times that in the prior austenite grains.

Abstract: A steel part having a long rolling contact fatigue life and capable of further increasing the life of a bearing under severer using condition than usual conditions. The steel part includes steel having a composition containing 0.7% by mass to 1.1% by mass of C, 0.5% by mass to 2.0% by mass of Si, 0.4% by mass to 2.5% by mass of Mn, 1.6% by mass to 5.0% by mass of Cr, 0.1% by mass to less than 0.5% by mass of Mo, 0.010% by mass to 0.050% by mass of Al, less than 0.0015% by mass of Sb as an impurity, and the balance composed of Fe and inevitable impurities, the steel being hardened and tempered. In the steel structure of a portion from the surface to a depth of 5 mm, residual cementite has a grain diameter of 0.05 to 1.5 ?m, prior austenite has a grain diameter of 30 ?m or less, and the ratio by volume of the residual austenite is less than 25%.

Abstract: A component for machine structural use having improved fatigue strength. The component for machine structural use is produced by subjecting at least a part of a steel material to hardening, and the hardened structure is controlled such that the average grain diameter of former austenitic grains is 12 ?m or less and the maximum grain diameter does not exceed four times the average grain diameter.

Abstract: The present invention provides a steel material for induction quenching, containing 0.3% to 0.7% of C, 1.1% or less of Si, 0.2% to 1.1% of Mn, 0.05% to 0.6% of Mo, 0.06% or less of S, 0.025% or less of P, 0.25% or less of Al, 0.3% or less of Cr on a mass basis, and the balance being Fe and unavoidable impurities. The steel material has a ferrite structure and a pearlite structure, the total volume fraction of the ferrite structure and the pearlite structure is 90% or more, the thickness of the ferrite structure is 30 ?m or less, and the average prior austenite grain diameter of a hard layer obtained by induction quenching is 12 ?m or less. Since having superior machinability and superior fatigue strength after induction quenching, this steel material is suitable, for an automobile drive shaft, constant velocity joint, and the like.

Abstract: There are provided a high dimensional accuracy pipe and a manufacturing method thereof, the pipe being in response to wide requirements of sizes, being manufactured at inexpensive cost, and having a sufficient fatigue strength. The detailed structure thereof is as follows. A push-to-pass process is performed in which, while a plug 1 is being charged in a metal pipe 5, the metal pipe is pushed in a hole provided in a die 2 and is then allowed to pass therethrough. As a result, a high dimensional accuracy pipe can be obtained in which at least one of the deviation of the outer diameter, the deviation of the inner diameter, and the deviation of the thickness in the circumferential direction is 3.0% or less as processed.

Abstract: The present invention provides a machine structural part composed of 0.3% to 0.7% of C, 0.30% or less of Si, 0.2% to 2.0% of Mn, 0.005% to 0.25% of Al, 0.005% to 0.1% of Ti, 0.05% to 0.6% of Mo, 0.0003% to 0.006% of B, 0.06% or less of S, 0.020% or less of P, 0.0030% or less of O on a mass basis, and the balance being Fe and unavoidable impurities. In addition, the machine structural part has a hard layer on at least a part of a surface thereof formed by induction quenching, an average prior austenite grain diameter of the hard layer is 7 ?m or less, and the maximum diameter of a non-metal inclusion composed of oxides is 15 ?m or less. Since having a high fatigue strength, this machine structural part is suitable for an automobile drive shaft, constant velocity joint, and the like.